Making the number of CPU cores used for sorting postings lists editable (#12247)

Signed-off-by: Yuri Nikolic <durica.nikolic@grafana.com>

tsdb/head.go

@@ -574,7 +574,7 @@ const cardinalityCacheExpirationTime = time.Duration(30) * time.Second
 func (h *Head) Init(minValidTime int64) error {
 	h.minValidTime.Store(minValidTime)
 	defer func() {
-		h.postings.EnsureOrder()
+		h.postings.EnsureOrder(h.opts.WALReplayConcurrency)
 	}()
 	defer h.gc() // After loading the wal remove the obsolete data from the head.
 	defer func() {

tsdb/index/postings.go

@@ -224,7 +224,10 @@ func (p *MemPostings) All() Postings {
 
 // EnsureOrder ensures that all postings lists are sorted. After it returns all further
 // calls to add and addFor will insert new IDs in a sorted manner.
-func (p *MemPostings) EnsureOrder() {
+// Parameter numberOfConcurrentProcesses is used to specify the maximal number of
+// CPU cores used for this operation. If it is <= 0, GOMAXPROCS is used.
+// GOMAXPROCS was the default before introducing this parameter.
+func (p *MemPostings) EnsureOrder(numberOfConcurrentProcesses int) {
 	p.mtx.Lock()
 	defer p.mtx.Unlock()
 
@@ -232,13 +235,16 @@ func (p *MemPostings) EnsureOrder() {
 		return
 	}
 
-	n := runtime.GOMAXPROCS(0)
+	concurrency := numberOfConcurrentProcesses
+	if concurrency <= 0 {
+		concurrency = runtime.GOMAXPROCS(0)
+	}
 	workc := make(chan *[][]storage.SeriesRef)
 
 	var wg sync.WaitGroup
-	wg.Add(n)
+	wg.Add(concurrency)
 
-	for i := 0; i < n; i++ {
+	for i := 0; i < concurrency; i++ {
 		go func() {
 			for job := range workc {
 				for _, l := range *job {

tsdb/index/postings_test.go

@@ -54,7 +54,7 @@ func TestMemPostings_ensureOrder(t *testing.T) {
 		p.m["a"][v] = l
 	}
 
-	p.EnsureOrder()
+	p.EnsureOrder(0)
 
 	for _, e := range p.m {
 		for _, l := range e {
@@ -114,7 +114,7 @@ func BenchmarkMemPostings_ensureOrder(b *testing.B) {
 			b.ResetTimer()
 
 			for n := 0; n < b.N; n++ {
-				p.EnsureOrder()
+				p.EnsureOrder(0)
 				p.ordered = false
 			}
 		})